How Grading Affects Foundation Drainage
Grading is the slope of the ground around a home. Proper positive grading directs rainwater and melting snow away from the foundation. Negative grading slopes toward the home and may allow surface water to collect beside the foundation wall.
A commonly accepted residential standard is a slope of at least 6 inches over the first 10 feet away from the foundation where site conditions allow. When that distance is unavailable, properly designed swales, drains, or other drainage methods may be needed to direct water away from the building.
Water collecting near the foundation may contribute to basement or crawlspace moisture, soil erosion, foundation movement, and deterioration of building materials. Persistent moisture may also create conditions conducive to mold growth, although grading alone does not establish that mold is present.
What Homeowners Should Look For
Walk around the exterior during or shortly after rainfall and look for water collecting beside the home, low areas near the foundation, soil erosion, or staining that suggests repeated water flow. Basement or crawlspace dampness, efflorescence, and elevated humidity may also indicate that exterior drainage should be evaluated.
Soil, mulch, and landscaping materials should not be piled against siding or other moisture-sensitive exterior materials. Appropriate clearance above grade varies by cladding material and manufacturer, but the lower edge should remain visible and separated from materials that may retain moisture.
Where the ground slopes toward the home or water repeatedly collects near the foundation, the grading and drainage should be evaluated and corrected by a qualified contractor. The completed work should direct surface water away from the building while maintaining appropriate clearance below the exterior cladding.